1. Field of the Invention
Exemplary embodiments of the present invention relate to a variable gain amplifier; and, more particularly, to a complementary metal-oxide semiconductor (CMOS) variable gain amplifier which has a wide linear-in-dB variable gain range to process an input signal having a wide range of magnitudes.
2. Description of Related Art
In a general communication system, a signal outputted from a transmitter is inputted to a receiver through a communication channel having various attenuation characteristics. At this time, in order to restore information transmitted from the transmitter from the inputted signal having a wide range of magnitudes, a process of controlling the inputted signal to a constant magnitude is required in the receiver. A function performed in such a process is referred to as an automatic gain control (AGC) function. A variable gain amplifier serves as a core block for realizing the AGC function. According to a paper published by John M. Khoury, “On the Design of Constant Settling Time AGC circuits”, IEEE Transactions on Circuits and Systems-II, vol. 45, No. 3, March 1998, pp. 283-294, the variable gain amplifier should have a linear-in-dB gain characteristic with respect to a variation in an inputted control signal, in order to obtain a constant settling time for input signals having a wide range of magnitudes in an AGC device.
Therefore, the gain variation range of the variable gain amplifier which may be used in the AGC device is limited to a linear-in-dB gain period. Accordingly, there is demand for the research and development of a CMOS variable gain amplifier having as wide a range of linear-in-dB gain characteristics as possible with respect to the variation of a control signal.
As demand for the CMOS variable gain amplifier having a wide range of linear-in-dB gain characteristics has increased, a communication system has been proposed. The communication system separately includes a converter configured to convert a control signal of which the magnitude is linearly varied into an exponential signal to exhibit the linear-in-dB gain characteristics, and then uses the exponential signal as a gain control signal of the variable control amplifier.
However, since a receiver of the communication system using the variable gain amplifier should additionally include the exponential signal converter configured to generate a linear-in-dB gain control signal in addition to the variable gain amplifier, it is difficult to implement a device having a low power consumption and a small integrated area.